The Condition

Feather pecking is behaviour which often leads to extensive damage to the plumage of laying hens. A more serious problem is one of abnormal aggressive feather pecking and cannibalism. This is one of the most worrisome problems on poultry units and is proving to be a problem on some large scale organic poultry farms (Lampkin, 1997). The various types of feather pecking are classified and the causes and prevention of feather pecking and cannibalism have been described by Savory (1995).

Feather pecking is not confined to domestic hens but is also common in pheasants, turkeys, partridges, parrots and a variety of other birds. The severity of feather pecking in poultry flocks can range from gentle feather pecking to an extreme and aggressive form recognised as cannibalism. A degree of feather pecking may be considered a natural preening process, but under deprived conditions it results in considerable health and welfare problems.

It is viewed by some as misdirected feed pecking, influenced by social dominance or "pecking order" and only occasionally associated with aggressive behaviour (Wennrich, 1975). Feather pecking is normally associated with back feathers, and may progress to the tail and the whole body. Aggressive pecking, however, is usually confined to the head.

Excessive feather pecking may be a consequence of a nutritional deficiency or unsatisfactory housing conditions that result in bullying. Overcrowding of birds in particular can encourage feather pecking. Organic systems, with low stocking rates, are likely to discourage this vice. However, under some conditions, excessive and aggressive feather pecking may be more common in free-ranging systems than battery systems. In battery systems there may be insufficient bird numbers per cage to allow hierarchical aggression.

Cannibalism may follow on from feather pecking, but may also arise independently. Cannibalism has been observed as starting with the pecking of fresh wounds in the back or excretory channels of a hen by nearby birds. This action is observed by other birds, who react similarly. Such pecking does not appear to be aggressive in character but to be part of normal feeding behaviour. The attacked birds are usually silent and make little attempt to escape. Pecking often continues until part of the intestine is obtained. Death follows, usually within 10 minutes, but pecking of the corpse continues.

Organic/free range systems

Permin and Nansen (1996) view the incidence of cannibalism, with the risk of secondary Escherichia coli infection, as a growing problem on organic farms. Keeling et al, 1988 observed an outbreak of cannibalism in a free-range flock that occurred primarily in the last 8 weeks of lay. Cannibalism and pecking have also been observed in other free range flocks in England (Swarbrick, 1986). Green et al (2000) conducted an extensive postal survey of "alternative" poultry systems in the UK and showed that over 55% of respondents reported feather pecking in laying flocks.

Most studies have been undertaken on caged battery hens and comparative studies have shown that the extent of feather pecking is worse in battery than free-range or deep-litter systems. Conversely, it has been shown, under some conditions, that non-caged birds are more at risk from cannibalism than in battery situations. The keeping of birds in large flocks or in systems where the bird comes into contact with excreta favours the development of microbial infection, parasitic infestation and cannibalism. This has been shown to be the case in aviary, high density, deep litter systems and straw yards (Loliger, Hagen, and Mathes, 1980; Loliger, 1985 and Gibson et al, 1988).

Flock size and density factors were also observed in research on laying hens in percheries, which showed that mild feather pecking increases with age, flock size and stocking density. However, although rare, aggressive pecking was most common in small flocks of low stocking density. This was related to birds attempting to form social hierarchies, whereas large flocks at high density appear to adopt non-social, non-aggressive behavioural strategies (Nicol et al, 1999).

Risk factors

The causes of feather pecking are closely linked with the nature of the environment in which the bird is kept (Hughes and Duncan, 1972). Although the causes of cannibalism are not fully understood, some of the predisposing factors listed in the Merck Veterinary Manual (1986) are overcrowding, excessive light and temperature, insufficient or improperly placed feeder or drinking space, nutritional imbalances including mineral deficiencies, feeding only pelleted or concentrated feed, feeding high energy diets heavy in corn or low in fibre, and injuries.

Green et al (2000) concluded that some of the factors associated with feather pecking included a low percentage of birds (less than 50%) using outdoor areas during fine and sunny days, the occurrence of egg peritonitis and infectious bronchitis. Other influential factors, possibly associated with inhibition of foraging and dust-bathing, included frequent changes of diet during laying, house temperatures of less than 20⁰C, increased lighting during inspection, and absence of loose litter at the end of laying and the use of bell drinkers.

Feeding

Feather pecking is exacerbated by feeding methods (Wennrich, 1975). Unlike wild birds, poultry are provided with a constant source of feed, and may therefore spend some time feather pecking. This is an important difference in feather pecking between ranging and caged hens. Free-range hens spend time foraging and less time pecking other birds. Feeding birds pellets also encourages feather pecking, as these can be eaten more rapidly.

Breed and type

Feather pecking and cannibalism are common in females and rare in males. Hughes (1973) implicated circulating hormonal balance as being an important factor. Cuthbertson (1980) showed a genetic influence, indicating some birds are more likely to feather peck than others. Offspring of hens who feather pecked are more inclined to show feather pecking behaviour than those from non feather pecking hens (Keeling and Wilhelmson, 1997). Feather peckers are also more active than non feather pecking birds.

Schlolaut and Lange (1977) showed differences between strains of White Leghorn hens. When birds selected under cage systems are raised on floors due to a change in consumer demand from cage-produced eggs to eggs from birds on floor production systems, as is the case in Denmark, there is increased cannibalism and feather pecking. Sorensen and Christensen (1997) discuss how this situation may have been the result of selection for egg production in fowls kept in cages which in turn may have resulted in a loss of genes for social interaction.

The more docile broiler breeds are rarely implicated, but the hybrid layers and turkeys are very susceptible. Chickens are by nature territorial and so due consideration must always be given to suitable stocking densities and the innate competition for food and water. Sorensen (1996) gives an account of the genetic effects on behaviour in fowls managed in cages or on the floor (including cannibalism and feather pecking), and discusses their importance for the selection of strains suitable for "ecological management".

Behaviour

Cannibalism has also been noted to start with vent pecking, frequently soon after a bird has finished laying, when the vagina is still partly open. The failure of pecked birds to escape has been associated with both ‘learned helplessness’ and affiliative behaviour. Learned helplessness is judged to be a state in which animals eventually become passive in reaction to suffering they cannot avoid. Affiliative behaviour is the flocking behaviour displayed by free-ranging hens, and includes the habit of pecking food off a bird that remains perfectly still. The failure to escape may be the result of birds being confused into this activity as a result of high levels of stocking (Appleby, Hughes and Elson, 1992).

The trigger for aggressive behaviour can be one or more of many factors. Attention to the management features will reduce the stress conditions which can trigger aggression, but other factors ranging from boredom to sub-clinical infections to the irritation of parasites like lice or mites can also be to blame. Feather eating, which is due to a nutritional protein and amino acid deficiency, can often lead to feather pecking and then to vent pecking.